KR20140087769A - Negative electrode for secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a negative electrode for a secondary battery including an electrode collector; a first coating layer that is applied onto a surface of the electrode collector and contains a negative electrode active material, a first aqueous binder, and a conductive material; and a second coating layer that is applied onto a surface of the first coating layer and contains a second non-aqueous binder. The negative electrode of the present invention is highly capable of buffering change in the volume of the negative electrode active material. Accordingly, cycle characteristics of a lithium battery can be improved in cases where the negative electrode of the present invention is adopted.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative electrode for a secondary battery, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a negative electrode for a secondary battery and a lithium secondary battery comprising the negative electrode. More particularly, the present invention relates to a negative electrode for a secondary battery capable of effectively improving degradation of a silicon-based negative electrode having a large volume change during charging and discharging, To a lithium secondary battery.

Recent developments in cell phones, camcorders, notebook PCs, and electric vehicles are increasing interest in energy storage technology. Among them, electrochemical devices have attracted the most attention, and rechargeable batteries that can be charged and discharged are of particular interest.

In particular, a lithium secondary battery using lithium and an electrolyte has been actively developed because of its high possibility of realizing a compact, lightweight, and high energy density.

Conventional lithium secondary batteries mainly use carbon-based compounds capable of reversible intercalation and elimination of lithium ions while maintaining structural and electrical properties as negative electrode active materials. Recently, it has been known that silicon, tin or an alloy thereof that causes a chemical reaction with lithium can reversibly store and release a large amount of lithium, and so much research is underway.

The silicon is promising as a high capacity anode material because its theoretical maximum capacity is about 4020 mAh / g (9800 mAh / cc, specific gravity 2.23) which is very large compared to graphite materials. However, the above-mentioned silicon or its alloys are disadvantageous in that the negative electrode is degraded by repeated expansion and contraction during charging and discharging, and the cycle life of the battery is lowered. That is, when lithium ions enter the anode active material (silicon) at the time of charging, the volume of the entire anode active material expands, resulting in a denser structure. Thereafter, at the time of discharging, the lithium ions are again discharged into the ionic state, and the volume of the negative electrode active material is reduced. At this time, since the components mixed together with the negative electrode active material have different expansions, voids are generated, and even the space-gaped portions are electrically disconnected and electrons are not smoothly moved. Further, when the elasticity of the binder mixed together with the negative electrode active material is lowered and cracks are generated, the electrical contact is blocked and the resistance is increased. This results in deterioration of the cathode and deteriorates the cycle characteristics of the secondary battery. This phenomenon is further exacerbated as the content of silicon, which is a high-capacity negative electrode active material, is increased in order to manufacture a cell having a high energy density.

In order to improve the above disadvantages, a method of increasing the binder content in order to increase the adhesion between the negative electrode active materials at the time of manufacturing the negative electrode has been attempted. However, this method has a disadvantage in that the content of the conductive material or the negative electrode active material is relatively lowered, the resistance characteristic of the battery is lowered, the conductivity is lowered, and the battery capacity and output are lowered.

On the other hand, in the case of the conventional carbon-based negative electrode, there is an example in which the content of SBR (styrene butadiene rubber) / CMC (carboxymethyl cellulose), which is an aqueous binder, is applied during the production of the negative electrode active material slurry. However, since such an aqueous binder forms a point-contact bond between adjacent anode active materials, there is a disadvantage that sufficient binding force can not be obtained between the silicone-based anode active materials repeatedly expanding and contracting.

Thus, there is a great need for a technology that improves the adhesion between the lithium metal oxide and the current collector while improving the electrical conductivity and performance of the secondary battery, such as capacity and output characteristics, while using an appropriate amount of binder.

An object of the present invention is to provide a negative electrode for a secondary battery comprising a coating layer made of a non-aqueous binder in order to effectively improve degradation of a silicon-based negative electrode having a large volume change during charging and discharging.

It is another object of the present invention to provide a lithium battery having improved cycle characteristics by including the negative electrode for a secondary battery.

Hereinafter, the present invention will be described in more detail.

In the present invention, in order to effectively improve degradation of a silicon-based negative electrode having a large volume change during charging and discharging, a negative electrode for a secondary battery, further comprising a second coating layer made of a non-aqueous binder formed on a surface or a whole surface of the first coating layer, .

Specifically, in the present invention,

Electrode collector;

A first coating layer coated on the electrode current collector, the first coating layer including a negative electrode active material, a first water-based binder, and a conductive material; And

And a second coating layer coated on the first coating layer, the second coating layer including a second non-aqueous binder.

In the negative electrode of the present invention, the electrode collector may be a surface treated with stainless steel, nickel, copper, titanium or an alloy thereof, copper or stainless steel with carbon, nickel, titanium or silver, Of these, copper or a copper alloy is preferable.

In the negative electrode of the present invention, the negative electrode active material which is a main component of the first coating layer may be carbon and / or carbon such as natural graphite, artificial graphite, expanded graphite, carbon fiber, hard graphitizable carbon, carbon black, carbon nanotube, fullerene, Graphite material; A metal such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt or Ti capable of forming an alloy with lithium and a compound including these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitride, and the like. However, the present invention is not limited to these. More specifically, examples of the negative electrode active material include a combination of one or more materials selected from the group consisting of crystalline carbon, amorphous carbon, a silicon-based active material, a tin-based active material, and a silicon-carbon based active material.

According to an embodiment of the present invention, the first aqueous binder included in the first coating layer is a component that assists in bonding to the negative electrode active material, the conductive material, and the current collector, 20% by weight. If the content of the first aqueous binder is more than 20% by weight, the area of the binder for bonding the negative electrode active material increases, thereby increasing the resistance.

Examples of such first water-based binders include one or more aqueous binders selected from the group consisting of styrene-butyl acrylate rubber (SBR), carboxymethylcellulose (CMC), and hydroxypropylcellulose have.

The conductive material may further comprise 1 to 20% by weight, based on the total weight of the first coating layer, as a component for further improving the conductivity of the electrode active material. Such a conductive material is not particularly limited as long as it can impart conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And conductive materials such as polyphenylene derivatives.

The first coating layer may further contain other additives in addition to the above-mentioned components, if necessary, and the specific content and amount of the first coating layer may be generally sufficient.

The first coating layer is a negative electrode active material layer formed by mixing a negative electrode active material, a first aqueous binder, a conductive material, and a solvent to prepare a first slurry, coating the current collector on the current collector, and drying the first slurry.

The solvent may be water.

The thickness of the first coating layer may be suitably changed according to the capacity design of the desired battery cell, and may have a thickness of several tens to several hundreds of microns.

The first binder may be coated on the entire surface of the negative electrode active material particles or may be coated only on the contact area between the negative electrode active material particles. Specifically, the first binder may be coated with an area that can maintain a proper bonding force while minimizing the resistance desirable.

In addition, according to one embodiment of the present invention, the second non-aqueous binder included in the second coating layer is excellent in wetting and permeability in the depth direction of the electrode, so that the bonding force between the negative electrode active material and the whole current collector Can be improved. The second non-aqueous binder is a chain polymer, for example, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), acrylonitrile-containing binder, polyvinyl alcohol, poly There may be mentioned a non-aqueous binder mixed with one or more selected from the group consisting of vinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene and polypropylene.

The second coating layer is formed as a binder coating layer by mixing a second binder and a solvent to prepare a second slurry, applying the dried second coating layer to a part or whole surface of the electrode coated with the dried first coating layer, and drying .

As the solvent, various solvents such as alcohols and ketones capable of dissolving N-methylpyrrolidone (NMP) or non-aqueous binder may be used.

The second coating layer is formed using a general coating method, and the forming method thereof is not particularly limited, and can be applied using a conventional dip coating method, spray coating method or the like.

The second coating layer including the second binder 15 may be applied to the entire surface of the electrode on which the first coating layer is formed or may be coated on the first binder 13 bonded to the point contact portion of the adjacent anode active material 11 (See Fig. 1). Specifically, it is preferable that the coating layer is coated with an area within a range capable of maintaining an appropriate bonding force. For example, the second coating layer may be present in an amount of up to about 100 weight percent, specifically from about 1 to 50 weight percent, more specifically from about 1 to 10 weight percent, based on the total weight of the electrode on which the first coating layer is formed , More specifically from about 1 to about 5 wt%, based on the total weight of the composition.

The second coating layer may further include a conductive material and other additives to improve conductivity.

In addition, the present invention provides a lithium secondary battery including the negative electrode, the positive electrode, the electrolyte, and the separator of the present invention and having improved charge / discharge characteristics and cycle characteristics.

The positive electrode may be prepared by applying a slurry containing a positive electrode active material, a conductive material and a binder on a positive electrode current collector by the same method as the negative electrode and drying the slurry. If necessary, the positive electrode slurry may further contain a filler.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may form fine irregularities on the surface to increase the adhesive force with the positive electrode active material. The positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; LiNi _{1 - xy} Co _x (Al) _y O ₂ wherein x = 0.15, Y = 0.05 oxide or Li _{1 + x} Mn _{2 - x} O ₄ where x is 0 to 0.33, LiMnO ₃ , Lithium manganese oxides such as LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _{1 -x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like can be used, but it is preferable to use LiNi _x Mn _{2 - x} O ₄ (x = 0.01 to 0.6), more preferably LiNi _{0 .5} Mn _{1 .5} O ₄ or LiNi _{0 .4} may be a Mn ₁ O _{4 .6.} That is, in the present invention, it is preferable to use a spinel lithium manganese composite oxide of LiNi _x Mn _{2 - x} O ₄ (x = 0.01 to 0.6) having a relatively high potential due to a high potential of the negative electrode active material as a cathode active material .

The conductive material may be added in an amount of 1 to 10% by weight based on the total weight of the slurry for the positive electrode, and is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, Graphite and other graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

Further, the binder is added as an ingredient for improving the bonding to the active material, the conductive material and the current collector, and usually 1 to 50% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include PVDF, which is a non-aqueous binder.

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

As the electrolyte solution, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used as the electrolyte solution containing a lithium salt, but the present invention is not limited thereto.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate , Gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, Derivatives, tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

Further, the separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used. Examples of such a separation membrane include an olefin-based polymer such as polypropylene, which is resistant to chemicals and hydrophobicity; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

 Also, the present invention provides a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack.

As described above, in the conventional negative electrode, the elasticity of the binder mixed together with the negative active material at the time of charging and discharging is lowered and the ability to buffer the change of the volume of the negative active material is insufficient. However, the negative electrode of the present invention, The binder coating layer including the second non-aqueous binder is further coated on the surface of the formed electrode to maintain a proper bonding force between the first coating layer and the collector and to buffer the volume change of the negative electrode active material during charging and discharging of the electrode, It is possible to manufacture a lithium secondary battery with improved cycle life and charge / discharge characteristics without increasing the resistance of the electrode.

In the present invention, by further forming a binder coating layer containing a non-aqueous binder on the negative electrode active material layer, it is possible to effectively prevent degradation of the silicon-based negative electrode having a large volume change during charging and discharging, Cycle characteristics can be improved.

1 is a schematic view of a negative electrode active material structure of the present invention.
2 is a graph showing the results of cycle retention measurement according to an embodiment of the present invention.
FIGS. 3A and 3B are graphs showing the capacity retention rate of the lithium secondary battery of the present invention obtained from Experimental Example 4. FIG.
4A and 4B are graphs showing the results of resistance characteristics tests of the lithium secondary battery of the present invention obtained from Experimental Example 4. FIG.

Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

I. The present invention For coating layer Slurry  Produce

(Production Example 1)

Polyacrylonitrile (PAN) (2 g) was dissolved in 100 mL of N-methylpyrrolidone (NMP) and stirred for 1 hour to prepare a second coating layer slurry.

(Production Example 2)

A slurry for a second coating layer was prepared in the same manner as in Preparation Example 1, except that polyvinylidene fluoride (PVDF) was used in place of the polyacrylonitrile (PAN).

(Production Example 3)

A slurry for the second coating layer was prepared in the same manner as in Preparation Example 1, except that an acrylonitrile-containing binder (X-linking agent) was used in place of the polyacrylonitrile (PAN).

II . Cathode manufacture

(Example 1)

12 g of a 5 wt% carbon nanotube (CNT) solution was dispersed while 35 g of a 1.2 wt% carboxymethylcellulose solution was stirred. Subsequently, SiO _x , a high-capacity negative electrode active material, and a stable charge- Graphite was added in a ratio of about 1: 2, and the active material was dispersed using a mechanical stirrer. Next, 2 g of a 40 wt% styrene butyl acrylate rubber (SBR) solution was mixed and finally stirred to prepare an active material, And a binder were mixed. (Here, the content of the binder in the first coating layer is within 7%.)

Subsequently, the slurry was coated on a copper (Cu) current collector using a comma coater to a thickness of about 100 탆, dried, and dried again under vacuum and at a temperature of 110 캜 to form a negative electrode plate .

Next, the slurry for the second coating layer prepared in Production Example 1 was applied to the surface of the negative electrode plate (first coating layer) on the negative electrode plate by a dip coating method and then dried to form a second coating layer Was prepared.

Subsequently, 45 wt% of LiNi _{1 - xy} Co _x (Al) _y O ₂ (where x = 0.15, y = 0.05) (NCA, Toda), 2.5 wt% of carbon black (Super- 2.5% by weight of fluoride / hexafluoropropylene copolymer (Solef 6020, Solvey) and 50% by weight of N-methylpyrrolidone were mixed to prepare a cathode active material composition, which was coated on the aluminum current collector to a thickness of 200 탆 And dried to prepare a positive electrode plate.

Next, LiPF ₆ was added to a solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3: 4: 3 to prepare an organic electrolyte solution having a lithium salt concentration of 1.2M.

Thereafter, polyethylene as a separator was disposed between the negative electrode plate and the positive electrode plate to form an electrode assembly, which was then placed in a battery case, and the electrolyte solution was injected to prepare a lithium secondary battery.

(Example 2)

A negative electrode plate and a secondary battery including the negative electrode plate were prepared in the same manner as in Example 1, except that the slurry for the second coating layer of Production Example 2 was applied instead of the slurry for the second coating layer of Production Example 1.

(Example 3)

A negative electrode plate and a secondary battery including the negative electrode plate were prepared in the same manner as in Example 1, except that the slurry for the second coating layer of Production Example 3 was used in place of the slurry for the second coating layer of Production Example 1.

(Comparative Example 1)

12 g (5% by weight) of carbon nanotube solution as a conductive material was dispersed while stirring 35 g of 1.2% by weight of carboxymethylcellulose solution. Next, SiO _x , a high-capacity negative electrode active material, and graphite having a stable charge-discharge behavior were added to the mixed solution at a ratio of about 1: 2, and the active material was dispersed using a mechanical stirrer. Subsequently, 2 g of a 40 wt% styrene butyl acrylate rubber solution was mixed and finally stirred to prepare a slurry for a first coating layer in which an active material, a conductive material and a binder were mixed. Subsequently, the slurry was coated on a copper (Cu) current collector with a thickness of about 100 μm using a comma coater, dried, and dried again under vacuum and at a temperature of 110 ° C. to prepare a negative electrode plate having a first coating layer.

Subsequently, 45 wt% of LiNi _{1 -x- y} Co _x (Al) _y O ₂ (where x = 0.15 is y = 0.05) (NCA, Toda), 2.5 wt% of carbon black (Super- 2.5% by weight of vinylidene fluoride / hexafluoropropylene copolymer (Solef 6020, Solvey) and 50% by weight of N-methylpyrrolidone were mixed to prepare a cathode active material composition, which was coated on the aluminum current collector in a thickness of 200 탆 And then dried to prepare a positive electrode plate.

Subsequently, LiPF ₆ was added to a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 3: 4: 3 to prepare an organic electrolyte solution having a lithium salt concentration of 1.2M.

Thereafter, polyethylene as a separator was disposed between the negative electrode plate and the positive electrode plate to form an electrode assembly, which was then placed in a battery case, and the electrolyte solution was injected to prepare a lithium secondary battery.

III . Adhesion and power experiment

(Experimental Example 1)

The anode plate prepared in Example 1 was cut at intervals of 10 mm and subjected to 180 ^o peel test to measure the adhesion force of the electrode coated with the second coating layer and the first coating layer, The results are shown in Table 1 and FIG.

(Experimental Example 2)

The adhesive force was measured in the same manner as in Experimental Example 1, except that the negative electrode plate of Example 2 was used in place of the negative electrode plate of Example 1, and the results are shown in Table 1 and FIG.

(Experimental Example 3)

The adhesive force was measured in the same manner as in Experimental Example 1, except that the negative electrode plate of Example 3 was used in place of the negative electrode plate of Example 1, and the results are shown in Table 1 and FIG.

(Comparative Experimental Example 1)

The adhesive force was measured in the same manner as in Experimental Example 1, except that the negative electrode plate of Comparative Example 1 was used instead of the negative electrode plate of Example 1, and the results are shown in Table 1 and FIG.

Cathode plate (% By weight) of the second coating layer, Adhesion (gf / 10mm) Example 1 4.2 128.1 Example 2 1.6 77.5 Example 3 4.2 107.0 Comparative Example 1 - 39.2

As shown in Table 1 and FIG. 2, in the case of the negative electrode plate in which the second coating layer of Examples 1 to 3 was formed, the adhesion between the second coating layer and the electrode formed with the first coating layer was improved, There is no significant difference in the cycle retention value even after the cycle. On the other hand, in the case of the negative electrode plate in which only the first coating layer of Comparative Example 1 is formed singly, the adhesive force is very low as 50 or less, There was a difference. Comparing the other discharge capacities to the cycle shown in FIG. 2, in the case of Comparative Example 1, the capacity retention rate after 300 cycles is very low, that is, 605 levels. In the case of Examples 1 to 3, %, And the lifetime is improved. On the other hand, it was found that the adhesion of the multilayer negative electrode plate having the second coating layer of the present invention is proportional to the amount of second coating (coating amount) applied on the first coating layer as shown in Table 1 above.

(Experimental Example 4)

The output and resistance of the secondary batteries manufactured in Examples 1 to 3 and Comparative Example 1 were measured using a hybrid pulse power characterization (HPPC) method.

The battery was charged from SOC 10 to a full charge (SOC = 100) up to 4.3 V at 0.1 C (4 mA), and the battery was stabilized for 1 hour. Then, the output and resistance of the lithium secondary battery were measured according to the HPPC test method. In addition, the battery was discharged SOC 10 to SOC 100 to SOC 10, and each battery was stabilized for 1 hour, and the output and resistance of the lithium secondary battery were measured by the HPPC test method for each SOC step.

The results of capacity retention after initial charge-discharge and 300 charge-discharge cycles are shown in FIGS. 3A and 3B, and resistance characteristics after initial charge-discharge and 300 charge-discharge cycles are shown in FIGS. 4A and 4B.

That is, as shown in FIGS. 3A and 3B, in the case of Comparative Example 1, the capacity retention rate after 300 cycles was as low as 60%, but in the case of Examples 1 to 3, the capacity retention rate was 80 %, And the lifetime is improved. 4A and 4B, in the case of Comparative Example 1, the resistance and the output value after 300 cycles fell in the entire SOC region as compared with the initial value. In Example 1, however, after 300 cycles, It can be seen that the resistance increase and the output decrease width are improved.

These results show that the second coating layer maintains the bond between the current collector and the first coating layer even during repeated charging / discharging by the second coating layer, thereby alleviating the change in the volume of the negative electrode active material, and thus the metallic active material and the current collector are electrically disconnected Can be prevented. Therefore, reversible storage / release of lithium ions can be maintained, and it is considered that cycle characteristics of the improved secondary battery can be obtained.

11: anode active material
13: first binder
15: Second binder

Claims (11)

Electrode collector;
A first coating layer coated on the electrode current collector, the first coating layer including a negative electrode active material, a first water-based binder, and a conductive material; And
And a second coating layer applied on the first coating layer and including a second non-aqueous binder. The method according to claim 1,
Wherein the first aqueous binder is one or more aqueous binders selected from the group consisting of styrene-butyl acrylate rubber, carboxymethylcellulose, and hydroxypropylcellulose. The method according to claim 1,
Wherein the first coating layer is present at a point-contact portion of adjacent anode active material particles, and binds the anode active material particles to each other. The method according to claim 1,
Wherein the second non-aqueous binder is selected from the group consisting of polyvinylidene fluoride, polyacrylonitrile, acrylonitrile containing binder, polyvinyl alcohol, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, and polypropylene. The negative electrode according to claim 1, wherein the binder is one or more selected from the group consisting of polyethylene and polypropylene. The method according to claim 1,
Wherein the second coating layer is coated on the entire surface of the electrode on which the first coating layer is formed or selectively coated on the first coating layer formed on the point contact portion of the adjacent anode active material particles. The method according to claim 1,
Wherein the second coating layer is coated in an amount of 100% by weight or less based on the total weight of the electrode on which the first coating layer is formed. The method of claim 6,
Wherein the second coating layer is coated in an amount of 1 to 50 wt% based on the total weight of the electrode having the first coating layer formed thereon. The method of claim 7,
Wherein the second coating layer is coated in an amount of 1 to 10 wt% based on the total weight of the electrode having the first coating layer formed thereon. The method of claim 8,
Wherein the second coating layer is coated in an amount of 1 to 5 wt% based on the total weight of the electrode on which the first coating layer is formed. The method according to claim 1,
Lt; RTI ID = 0.0 > 1, < / RTI > wherein the second coating layer further comprises a conductive material. A lithium secondary battery comprising the negative electrode, the positive electrode, the electrolytic solution and the separator according to claim 1.

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